Productive activity of society has brough a new dimension to the problems of the environment protection.
Accidental spillages of oil products, formation of slicks of surfactants on the water surface result in mass killing of fish, aquatic animals and plankton, pollution of coastal industrial zones and holiday resort areas. Undetected and non-eliminated oil and other slicks form water emulsions settling down to the water reservoir bottom and killing bottom plants. The harmful effect on the environment may be reduced by prompt detection and destruction of such slicks at any time day and night and under various weather conditions.
Contact methods were first used to detect water surface pollution such as sampling and subsequent analysis or a method of a floating capacitor based on measurement of capacitance between the layer of oil and water for oil slicks 0.5 to 6 cm thick, and the like. However, apparatuses employed for these purposes exhibit a very high sensitivity to high seas and feature a low response speed.
Later on remote (non-contact) methods came into use for detecting heterogeneity of water surface. A microwave radiometer was used as detector (cf. Bukharov M. V. Scientific Equipment of US Satellite SEASAT-1. Zarubezhnaya radioelectronika (in Russian), No. 8, 33-40). The radiometer is in the form of an aerial with a scanning means and a radiometric channel unit. Each radiometric channel comprises a series circuit including a switching member, a balanced mixer with an intermediate frequency amplifier, a square-law detector, a synchronous detector and a d-c amplifier. An output of the aerial system or reference or calibration radiation sources may be connected to one of the mixer inputs via the switching member. A heterodyne is connected to the other input of the mixer. Under working conditions, a signal to be measured is fed, via the switching member, to the mixer input where it is mixed with the heterodyne signal, the resultant signal being amplified. After the square-low and synchronous detection, an analog signal of the radiometric channel is formed at the output of the d-c amplifier. This signal carries information on temperature of the water surface. Temperature differences occur at heterogeneities of the water surface. Thus, in areas of pollution with oil products an increase in radio brightness temperatures occurs which makes it possible to ensure a rapid detection of such areas.
This apparatus cannot, however, be used for the detection of thin slicks of surfactants less than 100 .mu.m thick, and the detection results will materially depend on seas.
A new step in this direction was to use examination of infrared reflection spectra with the aid of lasers (cf. V. V. Bogorodsky, M. A. Kronotkin. Remote Detection of Oil Slicks with IR Laser. (in Russian). L., Gidrometizdat, 1975).
The apparatus comprises the following devices rigidly connected to one another: a laser having a mechanical chopper, a rotating plane mirror and a receiving and recording unit consisting of an optical focusing system, a bolometric receiver and a recorder. Laser radiation modulated at a pre-set frequency by means of the plane mirror is incident upon the water surface. The radiation reflected from the surface is directed to the radiation receiver by means of the optical focusing system. The signal from the bolometric radiation receiver is recorded by means of a voltmeter having a pointer or digital indicator at the output.
This apparatus is, however, strongly dependent on meteorological conditions where it is not possible to carry out mapping of a heterogeneity on the sea surface.
A further development in the class of these apparatuses is meteorological radar stations. Basic modes of operation of such radar stations are normal and contour scanning of meteorological formations, "image freezing" and radar mapping of the Earth surface. When working in the latter mode, various peculiar features of the Earth surface as well as oil slicks on the sea surface may be viewed on the indicator screen.
Such apparatus generally have an indicator built around a high-voltage TV-type cathode ray tube having intermediate characteristics in comparison with indicators built around normal and storage-type cathode ray tubes. An adequate brightness in such an indicator may be obtained by means of a raster scanning, and it is not absolutely necessary to make use of a luminphor with a long afterglow. During indication of radiolocation data, intermediate data (video signals) are stored during the period of direction scan.
It is preferred nowadays to use digital data storage since a memory with a maximum storage capacity of 10.sup.5 to 10.sup.6 bits is necessary for indication in meteorological radar stations. The use of such memory in indicators of meteorological radar stations is considered quite practical and warranted.
Known in the art is an apparatus for detecting heterogeneity of water surface (cf. Rev. "Meteorological Radar Stations of Civial Aviation US Aircraft" in Radioelektronika za rubezhom (in Russian). No. 14(856) 1978, pp. 14-16), comprising a transeiver, a data processor and an indicator built around a cathode ray tube which are connected in series with one another. The data processor consists of a driving generator having an output connected to an input of a control unit. The output of the control unit is connected to an input of a digital erasable memory, to an input of an integrating circuit and to an input of a sweep generator. The input of the integrating circuit is also a video signal input connected to the transceiver, and its output is connected to an input of an adder and comparator. The second input of the adder and comparator is coupled to an output of the memory, and an output of the adder and comparator is connected to a second input of the memory. An output of the memory is connected, via the sweep generator, to a beam sweep system and to an electrode controlling brightness of glow of the cathode ray tube in the indicator.
Video signals are fed in the digital form from the receiver output to the integrating circuit, they are integrated during several cycles and are then fed to the memory, via the adder and comparator. The memory is in the form of a shift register working in the erase and write mode. When new data arrive from the integrating circuit, they are compared in the adder and comparator with the data stored in respective cells of the memory. If these data are materially different, the new data will replace the data that have been stored in the memory.
As the aerial carries out direction scan, each of the pixels into which the screen is divided will either remain dark or glow with green colour at one of brightness values depending on intensity of precipitates that are "observed" by the aerial at a given moment. The control of the beam position is ensured by the memory which stores one bit for each pixel on the screen. The information stored in the memory is displayed on the screen at a frequency which is sufficient to avoid a strong flicker of image on the screen.
However, such apparatuses exhibit high quantizing noise during digital processing of a signal, and a limited memory capacity does not make it possible to accumulate an optimum number of direction scan cycles for the best detection of heterogeneity of water surface. Time-dependent automatic gain control systems available in such stations suppress the screen illumination by a signal diffused by a fine seas ripple, i.e. by a signal that carries basic information on heterogeneities at medium and short ranges. These radar stations are expensive and are made for aviation applications so that implementation of such tasks as oil slick detection is very expensive.